Improve _invalid_sequential_version msg.

[shayandavoodii]

This PR is created due to this discussion. When a version skipping happens, the RegistryCI shows the following message:

... . The following guidelines were not met:

Does not meet sequential version number guideline: version 1.3.2 skips over 1.3.1
Note that the guidelines are only required for the pull request to be merged automatically. However, it is strongly recommended to follow them, since otherwise the pull request needs to be manually reviewed and merged by a human.

In my opinion, this message gives the impression that version skipping is strictly prohibited. It seems to say that you should not do this, but if you did, you need to provide a convincing explanation for why you skipped some versions. Otherwise, the PR will not be merged. However, I can infer that the reason for this check is to prevent any mistakes rather than to ban version skipping. As Mr. Giordano stated:

lots of time [version skipping] is a mistake
a large fraction of [General registry] PRs closed without merge (not for new packages of course) is because of skipped versions which were a mistake.

However, the message I mentioned earlier could imply that developers who deliberately skipped some versions are doing something wrong or problematic, while the main purpose of this check is to prevent mistakes. Therefore, I opened this PR to improve the message. I appreciate your feedback and any suggestions you might have.

[ericphanson]

bors merge

[shayandavoodii]

Thank you so much for considering my proposal.

[DilumAluthge]

bors ping